Open vestibule being one that has the flaps open for ventilation. I would be more concerned about asphyxiation without having a vent to the outside for the spent gasses to go.

One of the reasons I like the TiGoat series is they come with chimneys and you can easily make almost any tent stove-ready. However, at $275+ to start they are not nearly as cheap as a couple of coffee cans. wink